Train wheel sensors are sensors installed on the inside of rails to detect whether or not train wheels pass by. At present, train wheel sensors are mainly classified into passive train wheel sensors and active train wheel sensors.
The working principle of a passive train wheel sensor is as follows: when train wheels pass by, the wheels cut the permanent magnetic field of the wheel sensor, so that a corresponding alternating signal is induced in the sensor coil, and a signal indicating that train wheels have passed by is provided. The passive train wheel sensors have the following major advantages that no external power supply is required when in use and few components are applied. However, the passive train wheel sensors have the following disadvantages that the magnitude of an output signal will vary along with the speed of a train. Particularly, the output signal is likely to be interfered when the speed of a train is lower than 5 km/h. As a result, the complexity of rear-end processing circuits is increased.
The working principle of an active train wheel sensor is as follows: a wheel signal is converted, by an active magnetic sensor inside the sensor, into a high level (there are wheels passed by) or low level (there are no wheels passed by) signal having a fixed magnitude. Generally, a wheel signal of a low-speed train can be identified. The active train wheel sensors have the following advantage that the output signal has a fixed magnitude. However, the active train wheel sensors need an external power supply to work, and are inconvenient in installation and maintenance; meanwhile, in harsh trackside environment, the power supply is likely to be damaged. As a result, the sensor has low reliability and relatively short mean time between failures.